1. Field of the Invention
This invention relates to a process for the preparation in high yield of a polybutadiene having a substantial proportion of syndiotactic-1,2 microstructure. More specifically this process involves the polymerization of 1,3-butadiene in the presence of a novel catalyst composition.
2. Related Prior Art
U.S. Pat. No. 3,778,424 discloses the preparation of 1,2-polybutadiene which is syndiotactic in character and uses for the polymerization of 1,3-butadiene a catalyst composition comprising: (a) a soluble cobalt compound; (b) an AlR.sub.3 compound in which R is a hydrocarbon radical of 1-6 carbon atoms and (c) CS.sub.2. The soluble cobalt compound is defined as including, among various other compounds, (1) a cobalt salt of an organic carboxylic acid of at least 6 carbon atoms, such as cobalt octoate and cobalt naphthenate and (2) a complex of a cobalt halide, such as CoCl.sub.2, with "a tertiary amine, e.g., pyridine, triethylamine, tributylamine and dimethylaniline . . . , and an N,N-dialkylamide, e.g., N,N-dimethyl formamide, N,N-dimethyl acetamide and N,N-diethyl formamide." The only such complex exemplified in the patent is the CoCl.sub.2 complex with pyridine.
In the above patent it is indicated that the prior art method of preparing syndiotactic 1,2-polybutadiene is unsatisfactory because of low yields as well as unsatisfactory physical properties. However, the best yield shown in the patent is in Table 5 where the control experiment shows a yield of 56%.
Marullo et al, U.S. Pat. No. 3,502,637 teaches the use of a catalyst system comprising a dialkyl aluminum halide and a solution of a cobalt compound which is a soluble complex of a normally insoluble salt of cobalt to polymerize conjugated dienes. As stated in Col. 7, lines 15-19, "The polymers of the conjugated diolefins obtained by the present method have substantially 1,4-enchainment of the monomer units and contain only a low proportion of vinyl groups. In general, the cis-structure prevails, as observed in the case of butadiene."
Marullo et al in U.S. Pat. No. 3,182,051 (Col. 1, lines 55-59) and in U.S. Pat. No. 3,300,466 (Col. 1, lines 45-58) make the statement "Thus by polymerizing butadiene in the presence of a catalyst containing a group 8 metal compound, such as a cobalt compound, and an alkyl aluminum halide, in any ratio of aluminum to group 8 metal, polymers having a substantially cis-1,4 structure are obtained." Both of these patents teach, however, that a combination of an aluminum trialkyl and a dialkyl aluminum halide may be used in which the combination contains 10-53% by weight of the dialkyl aluminum halide to polymerize butadiene to a syndiotactic-1,2 polymer. Nevertheless the teaching is that the alkyl aluminum halide per se, that is in the absence of a trialkyl aluminum compound, in combination with a cobalt compound, produces cis-1,4 polybutadiene.
Carlson et al in U.S. Pat. No. 3,066,127 shows the use of anhydrous cobalt compounds in combination with trialkyl aluminum, alkyl aluminum halides or alkyl aluminum hydrides produce polybutadiene of substantially all cis-1,4 structure. With controlled increased amounts of water, the cis-1,4 content decreases to 92% and with larger amounts of water the catalyst becomes inactive.
Carlson et al U.S. Pat. No. 3,135,725 likewise teaches the use of anhydrous cobalt compounds with trialkyl aluminum or alkyl aluminum halide compounds to give polybutadiene of substantially all 1,4 structure. With anhydrous materials, the polymer product has "little or no trace of trans-1,4 or 1,2 structures." "In most cases quite small variations in water content will also cause variation in the cis-1,4 and trans-1,4 content of the polymers." Consequently neither of these Carlson et al patents teach that there is anything other than a 1-4 structure produced in the polybutadiene when either trialkyl aluminum or an alkyl aluminum halide or an alkyl aluminum hydride is used in combination with a cobalt compound in a polymerization system.
In none of the above Marullo et al or Carlson et al patents is there any mention of COS nor of CS.sub.2. In each of these patents the polymer products is substantially all of 1,4 microstructure when an alkyl aluminum halide is used as the sole aluminum reducing component.
In the parent applications from which this present application is derived, the examiner has also cited the following: Harban U.S. Pat. No. 3,317,502; Fodor U.S. Pat. No. 3,635,930; Farson U.S. Pat. No. 3,317,494; Perry 3,813,374 and Sumitomo Japanese Pat. No. 3826,786. The Harban et al patent discloses the use of TiCl.sub.4 +AlR.sub.3 or alkyl aluminum halide with COS to polymerize olefins and Fodor discloses the use of TiCl.sub.3.AlCl.sub.3.AlR.sub.3 or alkyl Al halide with CS.sub.2 to polymerize olefins. Neither Harban et al nor Fodor mention butadiene or other dienes and therefore do not disclose the type of polymers that might be produced.
Farson and Perry both use TiCl.sub.4 plus AlR.sub.3 or alkyl Al halides to polymerize butadiene. Farson also uses CS.sub.2 and Perry also uses COS. Both processes produce cis-1,4 polymer.
The Japanese patent (Sumitomo) describes the use of TiCl.sub.4 with AlH.sub.2 X plus CS.sub.2 for the polymerization of olefins. No mention is made of butadiene and therefore no indication of the microstructure.
Consequently none of these additional references teach anything that would lead anyone to believe that anything other than a polymer of predominantly cis-1,4 structure would be obtained by the polymerization of butadiene with a catalyst system comprising a cobalt compound and a dialkyl aluminum halide as the sole reducing agent with or without COS.
Moreover, Halasa U.S. Pat. No. 3,993,856 shows that with the Co component and an alkyl aluminum dihalide, the use of CS.sub.2 gives cis-1,4-polybutadiene.